This invention relates to the production of a fuel from the pyrolysis or gasification of coal or oil shale. In particular, this invention relates to the production of a fuel from the pyrolysis or gasification of coal or oil shale in the presence of iron oxide in an inert gas atmosphere.
Petroleum shortages and inflated prices for petroleum products have provided incentives to develop alternate energy sources. The processing of coal or oil shale to produce an alternate fuel is an important method for attempting to satisfy global energy needs. Processes for the production of such alternate fuels include fluidized bed and fixed bed pyrolysis or gasification of coal and the like. In a conventional system, coal is pulverized and heated in a reactor system in which the coal undergoes pyrolysis or gasification. An inherent problem with the pyrolysis process occurs when particles of bituminous coal are heated. Heat causes the individual particles to soften and swell up to as much as several hundred percent of their original volume. Prior to swelling, the particles undergo a slight contraction. The swollen particles promote agglomeration or caking which causes the entire coal mass to swell. The formation of agglomerated material is enhanced by the pressure influences exerted on the coal by a fluidized or fixed bed system. The agglomeration of coal particles forms hard chunks of cementitious material that tend to clog and plug up the pyrolysis reactor system. Although operation at elevated pressures generally improves the economics of the pyrolysis process and facilitates the use of reactors with smaller volumes, the agglomeration problem tends to become worse as the operating pressure increases. Thus the agglomeration phenomenon has limited the use of otherwise advantageous elevated pressures.
Other disadvantages are associated with the coal agglomeration problem. The agglomeration problem limits the types of coal that can be processed by the system to noncaking types of coal. Additionally, this problem precludes the use of a high-pressure system since the high pressure would enhance the clogging of the reactor. An economically viable high-pressure system would increase the efficiency of the entire process. A further disadvantage relates to the resultant coke product which forms a solid residue which is difficult to reuse as fuel.
A similar problem is encountered during attempts to pyrolyze oil shale. There is a strong tendency for the shale particles to soften and become sticky. This leads to agglomeration which at best inhibits the efficiency of the pyrolysis reaction and reduces the yield and at worst results in plugging of the pyrolysis reactor.
The industry lacks a method for pyrolyzing coal or oil shale under high pressure which prevents the agglomeration of the coal particles. It would also be desirable to have a method for pyrolyzing coal which increases the quality of the resulting alternate fuel products.